Glazing technology and water-based glazing oil of

2022-08-08
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At present, UV glazing process and solvent based glazing process are widely used, while water-based glazing agent is rarely used. Glazing oil mainly includes solvent based and water-based. Solvent type is generally made of polyurethane, SBS (styrene butadiene styrene block copolymer), EVA (ethylene vinyl acetate copolymer), polyacrylate, etc. as the main resin, toluene, ethyl acetate, gasoline, etc. as the solvent, supplemented by tackifying resin, plasticizer, antioxidant and other additives. Due to the volatilization of organic solvents, there are shortcomings of flammability, toxicity and environmental pollution, which is no longer the focus of current research and development. Although UV glazing has the advantage of fast drying speed, it is expensive. The aqueous varnish formed by uniformly dispersing water-insoluble macromolecular substances in water through emulsifier overcomes the shortcomings of solvent based varnish, such as flammability, toxicity, high energy consumption, environmental pollution and so on, so it has become the focus of development and research in the field of paper glazing at present

classification of water-based Polish

1. Traditional water-based polish. The main agent of traditional water-based polish is polymer dissolved in water or suspended in water. Its water content is 50% - 70%. Due to the excessive water content, the glazing effect is not ideal, resulting in the problems of slow drying and difficult flow

2. New water-based polish. Adding additives (mainly surfactants) to the traditional water-based glazing oil forms a new type of water-based glazing oil. Among them, ethylene glycol or propylene glycol is used to replace 80% of water, and its appearance is milky white. By adjusting the solid content in the glazing oil, different glazing effects such as high gloss, ordinary gloss and sub gloss can be obtained

the new water-based glazing oil meets the requirements of health and environmental protection. It is used more and more, and is widely used in the packaging of food, medicine and other products. Moreover, the printing products using water-based glazing oil can be recycled through biodegradation

3. Catalytic waterborne polish. Catalytic waterborne Varnish is generally used in web printing machines with heating devices. It is thermosetting and will not be plasticized again when heated, so it can only be calendered by online calendering

catalytic waterborne Polish contains free formaldehyde, which is a carcinogen and harmful to human health. Therefore, from the perspective of sanitation and environmental protection, catalytic water-based glazing oil can only be used on printing materials that do not have high requirements for sanitation and environmental protection

composition and application of water-based glazing oil

water-based glazing oil is mainly composed of main agent, solvent and auxiliary agent

1. Main agent. The main agent of water-based glazing oil is film-forming resin, usually synthetic resin, which affects and dominates various physical properties and film evaluation in the deep layer. It is refined and implemented to the glazing quality of the operation team, machine and specific operators, such as gloss, adhesion, dryness, etc

there are many kinds of waterborne film-forming resins, but the copolymer resin of acrylic acid system is widely used at home and abroad. The performance of its copolymer resin depends on the composition of monomer and synthesis process. Waterborne acrylic copolymer resin has a series of excellent properties, such as good film-forming property, good gloss, high transparency, fast drying speed, wear resistance, water resistance and so on. It is widely used in Waterborne Varnish

2. Additives. Additives are used to improve the physical and chemical properties and processing characteristics of water-based varnish. The commonly used additives include: curing agent, surfactant, defoamer, desiccant, adhesion aid, wetting dispersant and additives. The use depends on the type of varnish. However, the amount of various additives should not exceed 5% of the total amount, otherwise it will affect the processing adaptability of glazing oil

3. Solvent. The main function of solvent is to disperse or dissolve synthetic resins and various additives

the solvent of water-based glazing oil is mainly water, which is colorless, tasteless, non-toxic, has a wide range of sources, low price, almost zero volatility, and very good leveling. However, there are also shortcomings, such as slow drying speed, easy to cause product size instability, etc. Therefore, an appropriate amount of ethanol is added during use to improve the drying performance of aqueous solvents and improve the processing adaptability of aqueous glazing oils

the application of water-based glazing oil must be comprehensively considered according to different glazing methods, paper types, product quality requirements, etc. in order to achieve good results. Attention should be paid when using:

① during the coating process, the viscosity and solid content of the glazing oil must be reasonably controlled, and the dilution can only be carried out within a certain range of solid content

② when selecting the paper type, it is necessary to effectively control the time. Considering the good dimensional stability of thick paper and poor dimensional stability of thin paper

③ it should be noted that the coating amount of water-based glazing oil is not easy to control, so the control of viscosity is very important

④ when using water-based varnish, you can completely cancel or reduce the use of anti stick dirt agent, because the water-based varnish is completely cured, the surface is very smooth, and rarely sticks dirty

⑤ in terms of the control of drying time, we should make full use of the osmotic drying of water-based glazing oil. Another way to improve the drying speed is to increase the content of ethanol, so I took out the Xinhua Dictionary and wrote down various meanings of one word, but it should be determined according to the actual situation and the viscosity of the glazing oil, and it cannot be adjusted at will

in a word, whether it is water-based glazing oil or other water-based materials, they are not very ideal in the printing of non absorbent substrate materials (on paper with good absorption, the printing adaptability is ideal), which needs to be further improved and perfected

the polishing of flexographic press is completed by the printing unit, so it can also be called printing light. Water based varnish can be used and degraded and absorbed by human body after 6 months, or UV drying system can be installed to use UV varnish. There are also special glazing devices for positive and negative glazing, which can also be used for the coating operation of non drying glue, and even machine compounding into non drying glue printing products, etc. The glazing coating is thicker than the printing ink layer to obtain better gloss or other effects

there are quite a lot of varieties of glazing (printing) materials, and choosing the appropriate varnish is a major factor to improve the quality of flexo printing products

flexographic printing usually needs to add one color water-based printing light or UV printing light at the end of the color sequence, which is completed by the printing unit. In addition to enhancing the gloss of the imprint, it is also to enhance the physical properties of the imprinted surface, so as to meet the needs of post press online processing and the practical requirements of commodity packaging, and become an essential process

① the full plate is printed by a special printing roller (rubber roller joint printing plate)

② local printing needs to be made into a printing plate and polished according to the required parts of the print

it should be pointed out that many packaging prints must use local printing light to meet the requirements of post press processing of products

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